UnsatisfiedLinkError invoke of native method

Question

Hi,
When the native method is invoked in the same Classloader as the native library is loaded, then everything is ok :-)
But when the native method is invoked in a "child" of the ClassLoader, which has loaded the native library, then a
java.lang.UnsatisfiedLinkError: <methodname>
is thrown.
Has anybody an idea?
Thank you for your assistance
Johannes Rameder

Answer 1

Hi,
Here is a small test example for solaris for better understanding.
I have tested this with solaris 9.
Put all files in a directory asst/test
---JNISmallTestHelper.java---
package asst.test;
public class JNISmallTestHelper {
  public JNISmallTestHelper() {
    printClassLoaderChain(this);
    JNISmallTest tmp = new JNISmallTest();
    int i = tmp.NoArgs();
    System.out.println("result of NoArgs is "+i);
  private static void printClassLoaderChain(Object o) {
    for (ClassLoader cl = o.getClass().getClassLoader(); cl != null; cl = cl.getParent()) {
      System.out.println("H: "+cl.toString());
---JNISmallTest.java---
package asst.test;
public class JNISmallTest {
  public JNISmallTest() {
    printClassLoaderChain(this);
  public native int NoArgs();
  private static void printClassLoaderChain(Object o) {
    for (ClassLoader cl = o.getClass().getClassLoader(); cl != null; cl = cl.getParent()) {
      System.out.println("J: "+cl.toString());
---JNISmallTestMain.java---
package asst.test;
import java.net.URL;
import java.net.URLClassLoader;
public class JNISmallTestMain {
  public JNISmallTestMain() {
    try {
      System.out.println("system "+ClassLoader.getSystemClassLoader());
      printClassLoaderChain(this);
      System.loadLibrary("JNITest");
      URLClassLoader ucl = new URLClassLoader(new URL[] {new URL("file:JNITest.jar")});
      ucl.loadClass("asst.test.JNISmallTestHelper").newInstance();
    } catch (Exception e) {
      System.out.println("Load exception " + e.toString());
      e.printStackTrace();
  public static void main (String[] args) {
    new JNISmallTestMain();
  private static void printClassLoaderChain(Object o) {
    for (ClassLoader cl = o.getClass().getClassLoader(); cl != null; cl = cl.getParent()) {
      System.out.println("M: "+cl.toString());
---JNITest.c---
#define JNITest_c
static char rcsid[] = "$Id:$";
#include <stdio.h>
#include <stdlib.h>
#include "JNITest.h"
JNIEXPORT jint JNICALL Java_asst_test_JNISmallTest_NoArgs (JNIEnv * env, jclass cls) {
   printf("*Called NoArgs in shared C library*\n");
   return 5;
---makeNOK.sh---
rm -rf *.class *.jar *.so *.o *.h TestMain
javac -classpath ../.. *.java
javah -classpath ../.. -o JNITest.h asst.test.JNISmallTest
cd ../..
jar cvf asst/test/JNITest.jar asst/test/JNISmallTestHelper.class asst/test/JNISmallTest.class
cd asst/test
rm JNISmallTestHelper.class
rm JNISmallTest.class
gcc -g -fPIC -I${JAVA_HOME}/include -I${JAVA_HOME}/include/solaris -c *.c
gcc -g -fPIC -shared -W1 --soname=libJNITest.so JNITest.o -o libJNITest.so
gcc -g -fPIC -L. -lJNITest TestMain.o -o TestMain
---makeOK.sh---
rm -rf *.class *.jar *.so *.o TestMain
javac -classpath ../.. *.java
javah -classpath ../.. -o JNITest.h asst.test.JNISmallTest
cd ../..
jar cvf asst/test/JNITest.jar asst/test/JNISmallTestHelper.class
cd asst/test
rm JNISmallTestHelper.class
gcc -g -fPIC -I${JAVA_HOME}/include -I${JAVA_HOME}/include/solaris -c *.c
gcc -g -fPIC -shared -W1 --soname=libJNITest.so JNITest.o -o libJNITest.so
gcc -g -fPIC -L. -lJNITest TestMain.o -o TestMain
---run.sh---
export LD_LIBRARY_PATH=.:/usr/lib:/usr/local/lib
echo "#start test with java"
java -cp ../.. asst.test.JNISmallTestMain
echo
echo "#start test with C"
TestMain
---TestMain.c---
#define testmain_c
static char rcsid[] = "$Id: TestMain.c,v 1.4 2004/03/16 20:20:54 neiExp $";
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
int main(int argc, char** argv) {
   printf("Calling NoArgs from C Main Program\n");
   printf("NoArgs returned %d to calling C program\n",
      Java_asst_test_JNISmallTest_NoArgs(0, 0));
   printf("After NoArgs call\n");
   exit(0);
}call makeOK.sh and run.sh
#start test with java
system sun.misc.Launcher$AppClassLoader@10dd1f7
M: sun.misc.Launcher$AppClassLoader@10dd1f7
M: sun.misc.Launcher$ExtClassLoader@53c015
H: java.net.URLClassLoader@108786b
H: sun.misc.Launcher$AppClassLoader@10dd1f7
H: sun.misc.Launcher$ExtClassLoader@53c015
J: sun.misc.Launcher$AppClassLoader@10dd1f7
J: sun.misc.Launcher$ExtClassLoader@53c015
Called NoArgs in shared C library
result of NoArgs is 5
#start test with C
Calling NoArgs from C Main Program
Called NoArgs in shared C library
NoArgs returned 5 to calling C program
After NoArgs call
Here you can see that the classloader which loads the native library is the same as the classloader which loads the class who invokes the native method.
then call makeOK.sh and run.sh
#start test with java
system sun.misc.Launcher$AppClassLoader@10dd1f7
M: sun.misc.Launcher$AppClassLoader@10dd1f7
M: sun.misc.Launcher$ExtClassLoader@53c015
H: java.net.URLClassLoader@108786b
H: sun.misc.Launcher$AppClassLoader@10dd1f7
H: sun.misc.Launcher$ExtClassLoader@53c015
J: java.net.URLClassLoader@108786b
J: sun.misc.Launcher$AppClassLoader@10dd1f7
J: sun.misc.Launcher$ExtClassLoader@53c015
Exception in thread "main" java.lang.UnsatisfiedLinkError: NoArgs
at asst.test.JNISmallTest.NoArgs(Native Method)
at asst.test.JNISmallTestHelper.<init>(JNISmallTestHelper.java:9)
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)
at java.lang.reflect.Constructor.newInstance(Constructor.java:274)
at java.lang.Class.newInstance0(Class.java:308)
at java.lang.Class.newInstance(Class.java:261)
at asst.test.JNISmallTestMain.<init>(JNISmallTestMain.java:18)
at asst.test.JNISmallTestMain.main(JNISmallTestMain.java:28)
#start test with C
Calling NoArgs from C Main Program
Called NoArgs in shared C library
NoArgs returned 5 to calling C program
After NoArgs call
The classloaders are different.